THE AERODYNAMICS OF A SPINNING SHELL. 
307 
given in § 1.2, the motion of a shell, of the shape used in these experiments, can be 
calculated with some approach to certainty. The general nature of the motion is 
described in 5 1.3. 
§ 1.2. The Numerical Results of the Experiments. 
We now proceed to give the numerical results obtained by analysis of the observa¬ 
tions by the methods explained in detail in Part IV. 
1.21. The Values of f M and f L . —-The observed values of / M and f L are shown 
plotted against v/a, in fig. 4, for the shell of external form A. # The value of fn is 
Fig. 4. Shells of form A. 
Curve I.—The couple coefficient / M (v/a) for 3-inch shells, with the centre of gravity 4-73 inches 
from the base. 
Curve II.—The same, with centre of gravity 4‘20 inches from the base. 
Curve III.—The drag coefficient f R {v/a) for comparison on ten times the scale. 
Curve IV.—The cross-wind force coefficient f L (v/a). 
The plotted points ©, A, □ show the observed values. The numbers denote the number of 
observations whose mean is represented by the plotted point. The stars distinguish those groups 
fired from the gun rifled one turn in thirty diameters. The others were fired from a gun rifled one 
turn in forty. 
* See fig. 6. Form A may be specified thus :—Length 3-84 shell diameters. Base cylindrical. Head 
with an ogive of 2 diameters radius. Centre of gravity 1 ■ 5 1 7 diameters from base. 
